Speed and torque control systems for internal combustion engines change throttle position and fuel injection amount to increase or decrease engine torque to a desired torque. Thus, during engine operating conditions where the actual delivered engine torque is greater than a driver requested engine torque, the throttle may be adjusted to decrease airflow to the engine. Accordingly, the fuel injection may be decreased. Because the throttle is coupled to the air intake valve of multiple cylinders through an intake manifold, there is a delay time before the change in throttle position results in a change in engine torque. Since adjusting the throttle position does not provide an immediate change in engine torque, the ignition timing is retarded to provide a faster response time. In the description herein, ignition timing may also be referred to as spark timing. Further, retarding ignition timing may also be referred to as spark retard. Therefore, the throttle position and ignition timing may both be adjusted to match the engine torque to the desired engine torque. In one example, spark retard may be employed in response to decreases in the driver requested engine torque. Thus, in order to provide a more instantaneous response to decreases in the desired engine torque, the ignition timing may be retarded.
In another example, spark retard may be employed when the driver requested engine torque increases from a level where fuel injection is off to a level where fuel injection is turned on. Under engine operating conditions where the desired engine torque drops below a threshold, such as during vehicle deceleration, fuel injection may be shut off and the vehicle wheels provide a force necessary to keep the engine running. This strategy is commonly referred to as deceleration fuel shut-off (DFSO), and provides improved fuel efficiency during low engine torque conditions. However, when the driver requested engine torque increases above the threshold where fuel injection is turned back on, the increase in engine torque resulting from the fuel injection may be greater than the driver requested increase in engine torque. As a result, in such conditions, the engine torque may exceed the desired engine torque. In order to reduce the delivered torque to more precisely match the driver requested torque in such conditions, spark retard may be employed.
The inventors herein have recognized that retarding ignition timing reduces fuel economy. In one example, some of the above issues may be addressed by a method comprising, as a desired engine torque increases, when not injecting fuel to engine cylinders, monotonically decreasing an alternator torque to a first level from a second level; and in response to the alternator torque reaching the first level, stepping up the alternator torque from the first level to the second level while initiating engine combustion, and then monotonically decreasing the alternator torque from the second level to the first level. In this way, less spark retard can be used, while still reducing delayed torque response and increasing energy capture in the vehicle battery.
In another representation, a method may comprise: during DFSO, when a throttle valve is in a first position and fuel is not injected to one or more engine cylinders, monotonically decreasing alternator torque to a first torque from a second torque as desired engine torque increases up to a first level, and during cylinder combustion, maintaining position of the throttle valve in a second position and monotonically decreasing alternator torque to the first torque from the second torque as desired engine torque increases from the first level to a second level. In some examples, the method may further comprise adjusting the position of the throttle valve between the second position and a third position as desired engine torque increases above the second level.
In another representation, the method may additionally comprise retarding spark timing from a desired spark timing during cylinder combustion, when the alternator torque is at the second level, and engine torque is greater than desired.
In this manner, fuel economy is improved by reducing the usage of spark retard, and a faster engine torque response time is provided by adjusting alternator torque in response to changes in a desired engine torque. Thus, the alternator torque may be used to adjust engine torque during both cylinder combustion, and when fuel is not being injected to the engine such as during a DFSO condition.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.